Project 1 SUMMARY/ABSTRACT Unfortunately, there are few ?druggable? alterations in high-grade serous ovarian cancer (HGSOC). Thus, exploration of therapeutic liabilities engendered by defects in homologous recombination (HR), the second most common aberration in ovarian cancer after TP53 mutation, has taken a dominant role. HR defects caused by germline and somatic BRCA1/2 aberrations, as well as aberrations in other pathway members, lead to synthetic lethality in combination with inhibition of poly (ADP-ribose) polymerase?1 (PARP). However, crucial gaps in knowledge exist that hinder our long-term goal of optimal implementation of PARP inhibitors (PARPi) including: 1) the identification of patients most likely to benefit from PARPi (i.e., ?PARPness?) and 2) the development of rational combination therapies able to prevent or overcome resistance to PARPi. In our prior SPORE project, we developed and implemented DNA, RNA and protein assays designed to predict benefit from PARPi as well as identified new members of the HR pathway, providing approaches to expand the population of patients likely to benefit from PARPi. In this SPORE proposal, we will complete our ongoing multi-arm combination trial with PARPi and phosphatidylinositol 3 kinase (PI3K) inhibitors and implement a resensitization trial in PARP resistant patients of Wee1 inhibition compared to PARP plus Wee1i. Using these trials, based on strong preliminary data from cell line, PDX and animal models, we will refine the utility of biomarkers to predict response and resistance to PARPi in HGSOC. We will further develop the preclinical and clinical data to justify a series of rational combination trials in this SPORE. Our overarching hypothesis is that the identification of a ?PARPness? molecular profile will expand the utility of PARPi in HGSOC. As a corollary, optimal outcomes will only manifest by rational combination therapy with PARPi. Thus, we will perform a systematic analysis of cell lines, animal models and patient samples, combined with our combinatorial adaptive resistance therapy platform and ultra-deep shRNA and CRISPR/CAS screens to targetable molecules to systematically identify rational combinations with PARPi therapy. To accomplish our long term goals and to test our overarching hypothesis, we propose two specific aims: Specific Aim 1: To identify and refine biomarkers of benefit from PARPi in ovarian cancer and Specific Aim 2: To establish a preclinical framework to identify and prioritize rational combination therapies in ovarian cancer. The successful implementation of the proposed studies will contribute to: 1) development of personalized treatment of women with advanced and recurrent ovarian cancer based on molecular profiles, 2) an expanded definition of patients likely to benefit from PARP inhibitors, 3) identification of resistance mechanisms to PARP inhibitors, and 4) rational combination therapies that will increase the spectrum of patients likely to benefit and also prevent the emergence of resistance. Successful implementation of this project will not only improve clinical outcomes but will direct development of future clinical trials to advance the field.